Apparatus and process for slag reduction in a vapor generator

ABSTRACT

The formation of slag is reduced on the heat absorption surfaces in the furnace section of a vapor generator. This is achieved by circulating a stream of air through the hopper section of the furnace.

United States Patent Winkin 51 May 16, 1972 [54] APPARATUS AND PROCESS FOR SLAG REDUCTION IN A VAPOR GENERATOR [72] Inventor: Justin P. Winkin, Fairlawn, NJ.

[73] Assignee: Foster Wheeler Corporation, Livingston,

[22] Filed: Oct. 9, 1970 [21] App]. No.: 79,581

[52] US. Cl ..122/235 R, 110/28 Q, 110/28 T, 122/235 M [51] Int. Cl ..F22l)' 37/00 [58] Field of Search ..110/28 Q, 28 T; 122/235 R, 122/235 M [56] References Cited UNlTED STATES PATENTS 1,792,068 2/1931 Caracristi ..1 10/28 T 2,586,790 2/1952 Dalinetal .j ..ll0/28Q FOREIGN PATENTS OR APPLlCATlONS 612,978 8/1926 France ..110/28Q 670,855 8/1929 France ..ll0/28Q Primary Examiner-Kenneth W. Sprague Attorney-John Maier, Ill, Marvin A. Naigur and John E. Wilson [ ABSTRACT The formation of slag is reduced on the heat absorption surfaces in the furnace section of a vapor generator. This is achieved by circulating a stream of air through the hopper section of the furnace.

2 Claims, 5 Drawing Figures FROM AIR PREHEATER 5 2 PATENTEDMAY 16 m2 SHEET 1 BF 2 FROM AIR PREHEATER 52 FIG.

INVI'JN'I'UII JUSTIN P. WINKIN W w ATTORNEY APPARATUS AND PROCESS FOR SLAG REDUCTION IN A VAPOR GENERATOR BACKGROUND OF THE INVENTION In the generation of power from fossil fuels, there has been a great deal of interest in the utilization of fuels containing relatively large concentrations of lignite. These types of fossil fuels have a high alkali metal content, and when they are burned, this usually results in severe slag deposits being formed on the heat absorption surfaces in the furnace section during the operation of the vapor generator. It has been found that severe slag on the furnace wall heat transfer surface occurs when the combined content of sodium and potassium in the fuel exceed 2 percent of the ash. Also, the slag problem can be further aggravated by the presence of calcium in the fuel.

In the past, slag formation has been achieved by restricting the use of lignite fuels to fuels having an alkali metal content of less than 2 percent of the ash which has been achieved by blending the lignite fuels. Also, additives have been used with the lignite fuel such as kaolin, and various types of deslagging devices have been provided, such as the injection of water under pressure against the heat transfer surfaces, as shown in applicants copending application Ser. No. 759,184 now U.S. Pat. No. 3,541,999. While the physical removal of the slag from the heat absorption surface of the furnace is important, it is possible to operate vapor generators at greater efficiencies by decreasing the incidence of slag formation in accordance with the present invention. Accordingly, it is possible to obtain superior heat transfer characteristics along the heat absorption surfaces of the furnace by reducing the frequency of employing water deslagging, thereby decreasing the attendant thermal stresses to such heat absorption surfaces. Also, by circulating air to the hopper section of the furnace, it is possible to obtain the added advantage of increased visibility in the hopper area of the unit to thereby allow the operators to have knowledge of potential slag build-ups in the lower furnace section. This affords the utilization of television cameras for remote viewing.

Through the present invention, means have been provided for reducing the incidence of slag formation by resorting to the introduction of excess air through the upper throat. It is preferable to utilize about 6 percent excess of the combustion air required for stoichiometric combustion through the hopper throat with a range of from 1 percent to percent excess air being operable. This air moves up along the hopper slopes and up between the burners. The small amount of air prevents recirculation of the gases in the hopper throat zone and creates an oxidizing atmosphere along the hopper slopes and the lower vertical portions of the front and rear walls of the furnace. Accordingly, this results in a substantial reduction of the slagging tendency in the furnace area.

It is important to be able to continuously operate coal fired vapor generators without slag fouling of the heat absorption surfaces. Accordingly, the present invention allows for the more efficient operation of vapor generators by reducing slag to build up in the lower portion of the furnace.

SUMMARY OF THE INVENTION In accordance with an illustrative embodiment demonstrating features andadvantages of the apparatus aspects of the present invention, there is provided an apparatus for reducing slag in the furnace section of a vapor generator. Accordingly, the hopper section of the furnace is formed with through ports and means are provided for conveying a stream of cooling air through the ports.

In accordance with an illustrative embodiment demonstrating features and advantages of the process aspects of the present invention, there is provided a process for reducing slag in the furnace section of a vapor generator in which openings are formed in the hopper section of the furnace. The process comprises conveying a stream of cooling air through the openings. This, the temperature in the furnace is lowered in order to reduce slag formation on the walls of the furnace seetion.

BRIEF DESCRIPTION OF THE DRAWINGS The above brief description as well as further objects, fea-v tures, and advantages of the present invention will be more fully appreciated by reference to the following detailed description of a presently preferred but nonetheless illustrative embodiments in accordance with the present invention when taken in connection with the accompanying drawings wherein:

FIG. 1 is a schematic sectional view of a vapor generator provided with means for conveying cooling air through the hopper section of the furnace;

FIG. 2 is a sectional view taken along the lines 2-2 of FIG. 1, showing the fin tube wall and wind box construction of the vapor generators;

FIG. 3 is an enlarged partial sectional view taken along the lines 3-3 of FIG. 1 to more clearly show the slotted openings in the hopper section;

FIG. 4 is an enlarged partial sectional view taken along the lines 44 of FIG. 1 to show the position of the slotted openings along the fin tube walls; and

FIG. 5 is a partial sectional view of an alternate wind box configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now specifically to the drawings, there is shown schematically in FIG. 1 a vapor generator 10 provided with a cooling air circulation system embodying features of the present invention and generally designated by the reference numeral 12. The vapor generator 10 includes a furnace section 14 capable of being fired with high alkali metal content fossil fuels and forming combustion gases which are passed through an upward vertical gas pass 16 to a horizontal gas pass 18. For the sake of brevity, the conventional downward vertical gas pass and stack have not been shown in the drawings. The vapor generator 10 is formed from insulated fin tube walls 22 which are in flow communication with a header system 24. As best seen in FIG. 1, the walls 22 of furnace section 14 include a front wall 26, rear wall 28, and side walls 30. The walls 22 of the vapor generator 10 are formed with an insulation section 32 and a fin tube wall section 34, with the fin tube wall section 32 forming interior heat absorption surfaces 36 which bound the interior periphery of the furnace section 14.

The vapor generator is provided with a burnersystem 40 which includes three opposing rows of individual burners 42 which have been shown in FIG. I, mounted in the front wall 26 and rear wall 28. The furnace section 14 includes a heavy slagging zone 43 which extends from the bottornportion of the furnace section 14 up to the top row of burners ,42. The burners 42 are conventional equipment used for the combustion of pulverized coal and for the sake of simplicity the means for igniting and feeding the fuel to the burners 42 are indicated schematically in FIG. 1 by the arrows 44. The burners 42 are mounted in a wind box 46 which is exteriorly attached to the front wall 26 and rear wall 28 of the furnace section 14. The wind box 46 extends downwardly from the burners 42 to a hopper section 48 and is connected in flow communication with a duct system 50 that is connected to a source of cooling air from an air preheater, designated 52. It should be noted that the hopper section 48 is conventionally formed with an inverted truncated cross section to allow for gravity expulsion of ash particles. The lower headers 24 are provided with seal ing plates 54 which extend into a conventional water sealed hopper 56.

Turning now to FIGS. 3 and 4, there is shown in detail the walls 22 of hopper section 48 which comprise tubes 60 to which there are welded on either side fins 62. The fins 62 are formed with slotted openings 64 for conveying a stream of cooling air, designated 66, to the furnace section 14. The throat area of the hopper section 48, along which the slotted opening 64 have been formed has been designated 68. Thus, by following the path of the directional arrows of cooling air stream 66 in FIG. 1, it can be seen that the cooling air passes through conduit 50 from the air preheater 52, into the wind box 46, and then through the openings 64 into the hopper section 48. In this manner, the cooling air circulation system 12 of the present invention results in a cooling air stream 66 that affords direct surface cooling along the heat absorption surfaces 36 of the hopper section 48, and also assures an air oxidizing atmosphere.

It should be noted that the elongated slots 64 are formed by removing the major portion of every other fin 62, as shown in FIG. 4. Thus, there is obtained a pattern of slotted openings 64 as shown in FIGS. 3 and 4.

In FIG. 5 there is shown another embodiment of the present invention in which corresponding parts have been designated by the same reference numerals as part of 100" series. In this form of the invention, there is shown a portion of a vapor generator 110 provided with a cooling air circulation system 112. The vapor generator 110 includes a furnace section 114 having heat absorption surfaces 136. There are exteriorly positioned on furnace section 114 three rows of burners 142, the top row of which defines a heavy slagging zone 143 which extends to the bottom of furnace section 114. The burners 142 are mounted in a wind box 146 which is positioned above the hopper section 148. Mounted below the wind box 146 is a duct system 150 for generating a stream of cooling air 166. The duct system 150 is in flow communication with wind box 146 and throat area 168. An adjustable valve 170 is provided in duct system 150 for controlling the volume of air in cooling air stream 166. It should be noted that the cooling air circulation system 112 is adapted for use in connection with certain types of vapor generators which do not have a wind box which extends below the hopper section as in the case of the vapor generator 10. Accordingly, in the vapor generator 110 a single conduit 150 can be provided for introducing a stream of cooling air 166 through the upper portion of the throat area 168. The remaining parts of vapor generator 110, which have not been shown in FIG. 5, are identical to the portions of vapor generator shown in FIGS. 2, 3, and 4.

By respectively introducing the stream of cooling air 66 and 166 into the furnace sections 14 and 114 through the slots 64, it is possible to reduce slag formation in the heavy slagging and ash particles in the furnace sections 14 and 114 so that the ash particles will have a reduced tendency to adhere to and build up on the heat absorption surfaces 36 and 136. It should be noted that the injection of gases containing excess oxygen, as in cooling air stream 66 and 166, has the additional salutary effect of maintaining an oxidizing atmosphere in the areas adjacent to or in contact with the heat absorption surfaces 36 and 136 in the furnace sections 14 and 114. Since the fusion temperature of ash particles is higher in an oxidizing atmosphere than in a reducing atmosphere, the tendency for slag formations to form on the heat absorption surfaces 36 and 136 is reduced if the atmosphere adjacent to these surfaces is maintained in an oxidizing state instead of a reducing state. Thus, in accordance with the present invention, by conveying the cooling air stream 66 and 166 into the hopper sections 48 and 148, the temperature in the zones 38 and 138 is lowered such that formation of slag on the heat absorption surfaces 36 and 136 is reduced.

A latitude of modification, change, and substitution is intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the spirit and scope of the invention herein.

What is claimed is:

1. Apparatus for reducing the temperature in the furnace section of a vapor generator including an air preheater, and formed with walls having an internal heat absorption surface and burners mounted on said walls, comprising a hopper section of said furnace formed with slotted openings, and means for conveying a stream of coolin air from said preheat er through said slotted openings suc that the temperature in said furnace section is lowered in order to reduce slag formation on the walls of said furnace section.

2. Apparatus according to claim 1, in which said vapor generator includes a wind box mounted on said furnace section, and a conduit extending from said wind box in flow communication with said hopper section for conveying said stream zones 38 and 138. The application of the stream of cooling air 40 ofcooling 

1. Apparatus for reducing the temperature in the furnace section of a vapor generator including an air preheater, and formed with walls having an internal heat absorption surface and burners mounted on said walls, comprising a hopper section of said furnace formed with slotted openings, and means for conveying a stream of cooling air from said preheater through said slotted openings such that the temperature in said furnace section is lowered in order to reduce slag formation on the walls of said furnace section.
 2. Apparatus according to claim 1, in which said vapor generator includes a wind box mounted on said furnace section, and a conduit extending from said wind box in flow communication with said hopper section for conveying said stream of cooling air. 